Our first attempt was to crystallize a baculovirus-expressed human type II TGF-beta receptor in complex with TGF-beta 1. Due to extensive glycosylation on the receptor, the crystallization trials with this receptor did not yield any crystals. Subsequent deglycosylation procedures yielded a partially deglycosylated receptor which produced small crystals when complexed with TGF- beta 1. However, these crystals diffract poorly in the X-ray beam and are not suitable for structure determination. To overcome the carbohydrate heterogeneity and low expression yield of the baculovirus expression system, we have cloned the soluble type II receptor gene into a bacteria expression vector. Due to a large number of disulfide bonds (12 cystines) present in this receptor, previous attempts by several groups to reconstitute the receptor have all failed. Our preliminary expression data suggests that approximately 20% of the protein is expressed in a non-aggregated soluble form and the rest is expressed in an inclusion body form using the bacteria system. The soluble part is shown to possess TGF-beta binding by ELISA assays. After in vitro reconstitution, the refolded receptor from the inclusion body material is also active in the ELISA assay. We have made several bacterial constructs with varying lengths in the N-terminal amino acid sequence of the type II TGF-beta receptor for crystallization. A similar construct corresponding to the full- length extracellular domain of the type I TGF-beta receptor was also made for protein expression and crystallization. We are refining the type I and II receptor bacteria expression systems to obtain large quantities of the receptor proteins for crystallographic studies. - TGF-beta receptor, crystal structure, protein expression, ELISA assay, cytokine